Insulating glass units (IGUs) are used in windows to reduce heat loss from building interiors during cold weather. IGUs are typically formed by a spacer assembly sandwiched between glass lites. A spacer assembly usually comprises a frame structure extending peripherally about the unit, a sealant material adhered both to the glass lites and the frame structure, and a desiccant for absorbing atmospheric moisture within the unit. The margins or the glass lites are flush with or extend slightly outwardly from the spacer assembly. The sealant extends continuously about the frame structure periphery and its opposite sides so that the space within the IGUs is hermetic.
There have been numerous proposals for constructing IGUs. One type of IGU was constructed from an elongated corrugated sheet metal strip-like frame embedded in a body of hot melt sealant material. Desiccant was also embedded in the sealant. The resulting composite spacer was packaged for transport and storage by coiling it into drum-like containers. When fabricating an IGU the composite spacer was partially uncoiled and cut to length. The spacer was then bent into a rectangular shape and sandwiched between conforming glass lites.
Perhaps the most successful IGU construction has employed tubular, roll formed aluminum or steel frame elements connected at their ends to form a square or rectangular spacer frame. The frame sides and corners were covered with sealant (e.g., a hot melt material) for securing the frame to the glass lites. The sealant provided a barrier between atmospheric air and the IGU interior which blocked entry of atmospheric water vapor. Particulate desiccant deposited inside the tubular frame elements communicated with air trapped in the IGU interior to remove the entrapped airborne water vapor and thus preclude its condensation within the unit. Thus after the water vapor entrapped in the IGU was removed internal condensation only occurred when the unit failed.
In some cases the sheet metal was roll formed into a continuous tube, with desiccant inserted, and fed to cutting stations where “V” shaped notches were cut in the tube at corner locations. The tube was then cut to length and bent into an appropriate frame shape. The continuous spacer frame, with an appropriate sealant in place, was then assembled in an IGU.
Alternatively, individual roll formed spacer frame tubes were cut to length and “corner keys” were inserted between adjacent frame element ends to form the corners. In some constructions the corner keys were foldable so that the sealant could be extruded onto the frame sides as the frame moved linearly past a sealant extrusion station. The frame was then folded to a rectangular configuration with the sealant in place on the opposite sides. The spacer assembly thus formed was placed between glass lites and the IGU assembly completed.
IGUs have failed because atmospheric water vapor infiltrated the sealant barrier. Infiltration tended to occur at the frame corners because the opposite frame sides were at least partly discontinuous there. For example, frames where the corners were formed by cutting “V” shaped notches at corner locations in a single long tube. The notches enabled bending the tube to form mitered corner joints; but afterwards potential infiltration paths extended along the corner parting lines substantially across the opposite frame faces at each corner.
Likewise in IGUs employing corner keys, potential infiltration paths were formed by the junctures of the keys and frame elements. Furthermore, when such frames were folded into their final forms with sealant applied, the amount of sealant at the frame corners tended to be less than the amount deposited along the frame sides. Reduced sealant at the frame corners tended to cause vapor leakage paths.
In all these proposals the frame elements had to be cut to length in one way or another and, in the case of frames connected together by corner keys, the keys were installed before applying the sealant. These were all manual operations which limited production rates. Accordingly, fabricating IGUs from these frames entailed generating appreciable amounts of scrap and performing inefficient manual operations.
In spacer frame constructions where the roll forming occurred immediately before the spacer assembly was completed, sawing, desiccant filling and frame element end plugging operations had to be performed by hand which greatly slowed production of units.
U.S. Pat. No. 5,361,476 to Leopold discloses a method and apparatus for making IGUs wherein a thin flat strip of sheet material is continuously formed into a channel shaped spacer frame having corner structures and end structures, the spacer thus formed is cut off, sealant and desiccant are applied and the assemblage is bent to form a spacer assembly.